Whaaaa that would be really cool actually
I’ve had tinfoils about how the walls of Wano were constructed, and I thought that Zuneshia might have been the key, since Ryuma is known for warding off the rest of the world which means they probably had no walls at that point. If Ryuma and Joyboy knew each other back then, Zuneshia might also have been the connection if it was the one to put up the walls since Zuneshia and Joyboy were buddies
I honestly have no idea what's going with Zuneshia, that Elephant is such a tease. The Pluton hype after 1055 is awesome, I can't wait to see the walls/borders come down.
Wait. If Ryuma was protecting Wano from invaders... and Ancient Wano is from 800 years ago like Sukiyaki said in 1055... then the border walls must have been placed 800 years ago, causing the flooding... SO IF RYUMA WAS PROTECTING WANO'S BORDERS FROM THE REST OF THE WORLD, THE COUNTRY HAD TO BE OPEN. If the borders were closed, it would have been easy to protect the country. RYUMA IS FROM ANCIENT WANO CONFIRMED. Welp, my headcanon just had fun.
I believe Joy Boy was Pluton. Oars could move continents. Joy Boy could create them, and was so strong that he could move tectonic plates themselves and form islands/landmasses. Joy Boy created Wano's borders..
So:
Joy Boy = Pluton = can move land (maybe by controlling animals like Zou?)
Shirahoshi = Poseidon = can move sea (using the sea kings)
Nami = Uranus = can move sky (this is why Nami is always connected to the sky/Moon)
Alright. Time to take a break from theories for a bit today